The present invention relates to closed-cell polymer foams, particularly to such foams that include an insulation-enhancing amount of an oil-containing furnace black, and more particularly, to a method of making such foams.
Carbon black, well known in the art as an effective infrared radiation absorber and reflector, has a conventional use as an additive in insulative foam structures to reduce thermal conductivity. However, the addition of carbon black often results in dispersion problems when manufacturing the foams. Such processing problems include increased pressure drop, higher foam density, increased open cells, and poor skin quality.
An attempt to solve some of these problems uses thermal grade carbon black (thermal black). For example, U.S. Pat. No. 5,373,026 discloses that thermal black processes easier, incorporates into a foam structure more readily, induces a lower process pressure drop, and has a lesser impact on polymer foam skin quality, all relative to other forms of carbon black.
Other attempts use carbon black coated with small amounts of a compatibilizing agent, such as a fatty acid, a phthalic ester, an oil, or a polyalkylene glycol, to enhance carbon black dispersion in both foam formulation and a resulting end-product foam. See U.S. Pat. No. 5,461,098; 5,397,807; and 5,571,847. However, compatibilizing agent addition involves an extra manufacturing step that increases foam production expense.
U.S. Pat. No. 5,710,186 uses titanium dioxide (TiO.sub.2) particles surface treated with a small amount of a wetting agent to enhance insulation capability of foams. The surface treated TiO.sub.2 grades cost more and provide less foam insulation performance improvement than carbon black.
Accordingly, a need remains for another cost-effective foam making method that provides enhanced insulation performance without adversely affecting foam processing or end product foam properties.